This invention relates to apparatus for protecting ceramic tiles and refractory rollers in roller tunnel kilns during the firing of said tiles.
In the production of tiles formed of ceramic or refractory material it is preferred to employ roller tunnel kilns for firing said tiles, the kiln consisting in a tunnel through which the tiles are advanced along a roller conveyor constituted by a stationary row of parallel, refractory rollers extending transversally to the longitudinal axis of the tunnel and individually rotated by light friction means about their own axis, at the same speed and direction of rotation.
Though roller tunnel kilns are preferred because of their high output and thermal efficiency, a frequent disadvantage occurs in the advancing of the tiles through the furnace zone and through the next cooling zone.
In the furnace zone, the rollers are stationary in position with respect to the advancing tiles, and they acquire a temperature greater than the temperature gained by the passing tiles and the temperature of the rollers in many cases exceeds the melting temperature of the ceramic or refractory material of the tiles. Consequently in the points of contact between the rollers and the passing tiles, the ceramic or refractory material is melted, even though the tiles are still allowed to advance into the furnace zone. However, when a melted tile enters the cooling zone, the molten material solidifies holding or welding the tile on at least a roller, impeding the rotation of the latter and thus the tile and the roller are stopped. In this event the successive tiles, arriving from the furnace zone, are stopped and they overlap each other or drop on the bottom of the kiln.
The overlapping creates extra weight on the rollers and may cause the breaking of the refractory rollers. In any case, the roller tunnel kiln has to be stopped and allowed to cool, so that a worker may enter through a provided manhole to remove the overlapped or dropped tiles, and, if necessary, replace the broken roller or rollers. The kiln is then again heated and the operation of the kiln is resumed. These operations require many hours during which the production is stopped.
A similar disadvantage is encountered because of drips of glaze material dropping on the refractory rollers, the glaze material being rendered semi-liquid along the furnace zone. In this event the glaze material dropped on the rollers stains the underface of the tiles and solidifies holding or welding the tile on, at least, a refractory roller.
In handling materials subject to said disadvantages, planar slaps of a refractory material have been employed, each supporting a discrete number of tiles, said planar slaps being themselves in contact with the refractory rollers.
The use of such slaps, however, incurs expenditure in purchasing them, in handling and in stocking them. Moreover they absorbed about 50% of the thermal energy supplied to the roller tunnel kiln, so the thermal efficiency of the kiln is very low.